In the proposed research, factors associated with the major causes of treatment failure following transplantation for patients with severe combined immunodeficiency disease (SCID) will be investigated: posttransplant infection, graft-vs-host disease, interstitial pneumonitis, aspiration pneumonia and de novo malignancies. Also, those factors that are associated with successful transplantation for SCID will be determined, i.e., full immunological reconstitution with disease-free survival. Finally, the degree of donor/recipient homology at HLS that is required to enable donor T lymphocytes to cooperate with host B lymphocytes in the 25% of transplanted SCID patients that exhibit split chimerism will be evaluated. The studies will utilize detailed information that has been reported to the International Bone Marrow Transplant Registry (IBMTR) regarding Greater than 190 SCID patients who received Greater than 260 transplants. Multivariate statistical analyses, that take into account and adjust for other variables, will be used to examine the importance of Greater than 45 pre- and posttransplant prognostic factors. The IBMTR data base is a unique resource in that it represents the only large collection of comprehensive data on transplantation for SCID available in the world. This fact, plus the unique characteristics of the disease itself, present an opportunity to investigate several basic immunobiological questions that could otherwise not be studied in humans.